“Gas operated” firearms, such as semi-automatic firearms, typically utilize internal bore pressures and/or combustion gases bled from the barrel of the firearm during the firing of a round of ammunition to drive the action system of the firearm. Typically, the action system of the firearm will include an action sleeve assembly or slide that attaches to and communicates with the bolt assembly of the firearm. During operation, upon firing, combustion gases are diverted from the barrel of the firearm to the action system via a series of ports, which are typically cylindrical holes machined in the wall of the barrel. The diverted combustion gases generally force the action sleeve assembly rearward to a stopping point at a rear limit, so that the spent round is ejected; the hammer is moved to a cocked, ready position; and a new round of ammunition loaded into the chamber of the firearm as the action system is closed.
The combined volume of the ports in the barrel regulates the amount of gas and thus the amount of energy that is transmitted to the action system of the firearm. However, a problem exists for firearms that are chambered for cartridges or shot shells, that, within a particular caliber or gauge, can have greatly varying ammunition offerings (i.e., firing magnum loads versus lighter target loads in shotguns, rifles and other types of firearms), such that controlling the energy and/or movement of the action system of the firearm solely by gas port volume is not practical. For example, lighter energy producing loads that result from target loads for shot shells, generally require significantly larger port sizes than higher energy producing loads in order to provide a sufficient volume of gas to drive the action system. Consequently, port geometry in gas operated firearms typically has been set up to accommodate the lightest energy producing loads, i.e., having larger ports, with compensation devices being added to the action system in an attempt to reduce the energy transmission to the action system when higher energy producing ammunition is used.
Compensation devices have typically included spring-loaded pressure relief valves, which are activated upon the operating energy or gas pressure in the system exceeding a predefined pressure, typically provided by the spring, upon which the compensation or pressure relief valve will be opened and a portion of the excess energy/gas bled off or released. Although such compensation systems can reduce input energy (gas pressure), there still remains a substantial difference in the energy available to drive the action system of the firearm. In general, bolt velocity is used as a relative measure of the amount of energy directed to the action system, with the higher the bolt velocity, the more energy that is being directed to the action system.
FIG. 1 generally illustrates a bolt velocity comparison for both high and light energy-producing ammunition rounds in a conventional, compensated, semi-automatic shotgun. As indicated in FIG. 1, there is a significant variation in the peak bolt velocities and in the terminal velocities of the action system in such a conventional compensated firearm for different types of ammunition used. Typically, higher energy-producing rounds, such as magnum rounds, will have a very high peak velocity, e.g., upwards of 400 inches per second. This bolt velocity remains fairly steady through the entire stroke and does not drop off until the bolt is moved to its rear limit and further movement thereof is stopped. Peak velocities for the lighter-producing energy rounds generally are not as high as for the high energy-producing rounds, and are typically only 300 inches per second and tend to remain fairly steady over a longer length of time. In other words, conventional compensation systems typically hit a peak and then remain fairly constant throughout the stroke or cycle of the firearm until it impacts the rear of the receiver and then an abrupt and potentially damaging stop occurs. For both lighter energy-producing rounds and higher energy-producing rounds, the amount of energy put in is limited, but it does not dissipate throughout the stroke.
For semi-automatic firearms, an optimum design would be one that provides consistent bolt velocity profiles regardless of the type of ammunition shot in the firearm, and that will operate with enough energy to ensure a full stroke with a minimum terminal velocity. Upon firing, the velocities at which the action system is translated or moved affects the timing of the various mechanical interactions resulting from operation of the action system, and variations in such velocities can lead to potentially serious malfunctions of the firearm components. Excess terminal velocity can lead to premature fatigue of various components of the firearm, while at full stroke, excess action system energy (velocity), such as generated by high energy rounds, must be consumed or addressed. The consumption of excess energy typically is accomplished through a jarring mechanical impact as the bolt assembly and action system of the firearm are stopped at the rear limit of the action sleeve assembly. Although buffers have been incorporated to soften the impact, the rapid decline in action system velocities still typically will impart substantial inertial loading on the components, potentially causing premature fatigue and failure when higher energy ammunition is shot in large quantities.
Accordingly, it can be seen that a need exists for an action rate control system for a firearm that addresses the foregoing and other related and unrelated problems in the art.